U.S. patent application number 10/689430 was filed with the patent office on 2005-04-21 for contaminant particle removal by optical tweezers.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co.. Invention is credited to Chen, Hong-Miao, Jong, Yu-Chang, Tseng, Huan-Chi.
Application Number | 20050081824 10/689430 |
Document ID | / |
Family ID | 34521410 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050081824 |
Kind Code |
A1 |
Chen, Hong-Miao ; et
al. |
April 21, 2005 |
Contaminant particle removal by optical tweezers
Abstract
The invention describes how contaminant particles may be removed
from a surface without in any way damaging that surface. First, the
positional co-ordinates of all particles on the surface are
recorded. Optionally, only particles that can be expected to cause
current or future damage to the surface are included. Then, using
optical tweezers, each particle is individually removed and then
disposed of. Six different ways to remove and dispose of particles
are described.
Inventors: |
Chen, Hong-Miao; (Hsin-Chu
city, TW) ; Jong, Yu-Chang; (Hsin-Chu city, TW)
; Tseng, Huan-Chi; (Hsin-Chu city, TW) |
Correspondence
Address: |
DUANE MORRIS, LLP
IP DEPARTMENT
ONE LIBERTY PLACE
PHILADELPHIA
PA
19103-7396
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co.
|
Family ID: |
34521410 |
Appl. No.: |
10/689430 |
Filed: |
October 20, 2003 |
Current U.S.
Class: |
123/399 ;
134/1.3; 438/115 |
Current CPC
Class: |
Y10S 438/906 20130101;
B08B 7/0042 20130101; H01L 21/02046 20130101 |
Class at
Publication: |
123/399 ;
134/001.3; 438/115 |
International
Class: |
H01L 021/44; C25F
001/00; C25F 003/30; C25F 005/00; B08B 006/00; H01L 021/48; H01L
021/50; F02D 001/00 |
Claims
What is claimed is:
1. A process for removing contaminants from a surface of a
semiconductor wafer, comprising: providing a source of laser light
and a lens system capable of focusing said laser light to a focal
point; obtaining positional co-ordinates, on the wafer surface, for
a particle; using said positional co-ordinates, placing the lens so
that the focal point is directly in line with said particle and at
a distance therefrom; passing said laser light through the lens at
a power level sufficient to form, at said focal point, an optical
trap into which said particle is drawn; and disposing of the
particle while reducing the power level until the particle is drawn
out of the trap by gravitational forces whereby it is not returned
to the wafer surface.
2. The process described in claim 1 wherein the particle has a mean
diameter less than about 1 micron.
3. The process described in claim 1 wherein the lens system has a
numerical aperture greater than about 0.8.
4. The process described in claim 1 wherein the power level of the
laser is at least about 10 W.
5. The process described in claim 1 wherein the lens system may
also is used for obtaining said positional co-ordinates.
6. The process described in claim 1 wherein said surface further
comprises an integrated circuit and said positional co-ordinates
are such that the particle has a non-zero probability of damaging
said circuit.
7. (canceled)
8. The method of claim 1 wherein said distance between the particle
and the focal point is between about 200 and 500 nanometers.
9. A process for removing contaminant particles from a
downward-facing surface of a semiconductor wafer, comprising:
providing a source of laser light and a lens system capable of
focusing said laser light to a focal point; obtaining positional
co-ordinates, on the wafer surface, for a set of said particles;
providing a stream of gas that flows past and around the wafer in a
downward direction; performing the sequential steps of: (a) using
said positional co-ordinates, placing the lens so that the focal
point is directly below a particle of the set at a distance
therefrom; (b) passing said laser light through the lens at a power
level sufficient to form, at said focal point, an optical trap into
which said particle is drawn; (c) reducing said power level whereby
the particle is removed through a combination of gravitational
forces and said stream of gas; and repeating steps (a), (b), and
(c) for all other member of the set of particles.
10. The process described in claim 9 wherein the particles have
mean diameters less than about 1 micron.
11. The process described in claim 9 wherein the lens system has a
numerical aperture greater than about 0.8.
12. The process described in claim 9 wherein the power level of the
laser is at least about 10 W.
13. The process described in claim 9 wherein said distance between
a particle and the focal point is between about 200 and 500
nanometers.
14. The process described in claim 9 wherein the set of particles
consists of all particles on the wafer surface.
15. The process described in claim 9 wherein said surface further
comprises an integrated circuit and the set of particles consists
of all particles that have a non-zero probability of damaging said
circuit.
16. A process for removing contaminant particles from an
upward-facing surface of a semiconductor wafer, comprising:
providing a source of laser light and a lens system capable of
focusing said laser light to a focal point; obtaining positional
co-ordinates, on the wafer surface, for a set of said particles;
performing the sequential steps of: (a) using said positional
co-ordinates, placing the lens so that the focal point is directly
above a particle of the set at a distance therefrom; (b) passing
said laser light through the lens at a power level sufficient to
form, at said focal point, an optical trap into which said particle
is drawn; (c) disposing of the particle by moving the focal point
until it is no longer above the wafer surface and reducing said
power level whereby the particle is removed by gravity and not
returned to the wafer surface; and repeating steps (a), (b), and
(c) for all other member of the set of particles.
17. (canceled)
18. The process described in claim 16 wherein the step of disposing
of the particle further comprises: increasing the distance between
the focal point and the wafer surface; inserting a catcher plate
between the focal point and the surface; reducing said power level
whereby the particle falls onto the catcher plate; and removing the
catcher plate.
19. The process described in claim 16 wherein the step of disposing
of the particle further comprises moving the wafer until it is no
longer beneath the focal point and then reducing said power level
whereby the particle is removed by gravity.
20. The process described in claim 16 wherein the step of disposing
of the particle further comprises: providing a tube having a first
end that is open and a second end that is connected to a container
maintained at a pressure lower than that at the focal point; and
positioning the tube so that said open end is near the particle
being held in the light trap, thereby sucking the particle out of
the light trap into said low pressure container.
21. The process described in claim 16 wherein the step of disposing
of the particle further comprises: providing a tube having a first
end that is open and a second end that is connected to a source of
pressure that is higher than that at the focal point; and
positioning the tube so that said open end is near the particle
being held in the light trap, thereby blowing the particle out of
the light trap and away from the wafer.
22. The process described in claim 16 wherein the set of particles
consists of all particles on the wafer surface.
23. The process described in claim 16 wherein said surface further
comprises an integrated circuit and the set of particles consists
of all particles that have a non-zero probability of damaging said
circuit.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the general field of integrated
circuit manufacture with particular reference to the removal of
contaminant particles.
BACKGROUND OF THE INVENTION
[0002] Contaminant particles are among the most common problems
associated with IC (integrated circuit) manufacturing processes.
They may cause device yield loss because of photo defocus in
successive layers, pattern bridging, contact/via opens, CMP
(chemical mechanical polishing) scratching, etc. Current in-line
inspection tools, such as KLA (an on-line defect inspection tool
produced by KLA-Tensor) make it easy to accurately determine the
location and size of contaminant particles on wafers but there is
no tool for removing these particles except scrubber cleaners.
Unfortunately, scrubber cleaning is not a suitable method for
dielectric layers, patterned layers, water-absorbent layers, metal
layers (corrosion concern), etc and the device yield loss remains
the same even though we know the position of these contaminant
particles.
[0003] Optical traps, sometimes referred to as optical tweezers,
utilize a light source to produce radiation pressure. Radiation
pressure is a property of light that creates small forces by
absorption, reflection, or refraction of light by a dielectric
material. Relative to other types of forces, the forces generated
by radiation pressure are almost negligible-only a few picoNewtons.
However, a force of only a few picoNewtons is sufficient to allow
attachment to particles of the sizes just discussed.
[0004] Optical tweezers utilize the force that exists when a
transparent material with a refractive index greater than the
surrounding medium is placed in a light gradient. As light passes
through polarizable material, it induces a dipole moment. This
dipole interacts with the electromagnetic field gradient, resulting
in a force directed towards the brightest region of the light,
normally the focal region. Conversely, if an object has a
refractive index less than the surrounding medium, such as an air
bubble in water, the object experiences a force drawing it toward
the darkest region.
[0005] As long as the frequency of the laser is below the natural
resonances of the particle being trapped, the dipole moment will be
in phase with the driving electric field. A schematic view of a
light tweezer setup is illustrated in FIG. 1. Light 11, typically
laser light, enters a high numerical aperture objective lens 12 of
an optical system and is focused 16 to a diffraction limited region
(spot) 13 on a particle 14. Because the intensity profile of the
laser light is not uniform, an imbalance in the reaction forces
generates a three-dimensional gradient force 15 with the brightest
light in the center. The gradient force 15 pulls the object toward
the brightest point. Thus, the forces generated by the optical
system "traps" the object. Such gradient forces are formed near any
light focal region.
[0006] The sharper or smaller the focal region 13, the steeper the
gradient. To overcome scattering forces near the focal region and
hence prevent the object from being ejected along the direction of
the light beam, the optical system must produce the steepest
possible gradient forces. Sufficiently steep gradient forces can be
achieved by focusing laser light to a diffraction-limited spot
through a microscope objective of high numerical aperture
(N.A.).
[0007] A routine search of the prior art was performed with the
following references of interest being found:
[0008] In U.S. Pat. No. 6,055,106, Grier et al. describe an
apparatus for manipulating small dielectric particles. In U.S. Pat.
No. 5,953,166, Shikano discloses a laser trapping apparatus while
in U.S. Pat. No. 5,689,109 Schutze discloses an apparatus and
method for the manipulation, processing and observation of small
particles. Weetall et al., in U.S. Pat. No. 5,620,857 use tightly
focused laser beams as optical tweezers while Burns et al., in U.S.
Pat. No. 5,245,466, create arrays using light beams coupled to
microscopic polarizable matter. U.S. Pat. No. 5,079,169 is a method
for optically manipulating polymer filaments. Ashkin et al.
describe a nondestructive optical trap for biological particles in
U.S. Pat. No. 4,893,886. Finally, in U.S. Pat. No. 5,512,745, Finer
et al. shows an optical trap system while Ashkin (U.S. Pat. No.
3,808,550), and Shivashankar et al. (U.S. Pat. No. 6,139,831) show
optical trap related patents.
SUMMARY OF THE INVENTION
[0009] It has been an object of the invention to remove contaminant
particles from a surface.
[0010] Another object of the invention has been that the act of
removing said particles not damage the surface in any way.
[0011] A further object has been that the invention allow a choice
to be made between removing all particles on the surface and
removing only particles that have the potential to damage the
surface.
[0012] These objects have been achieved by first recording the
positional co-ordinates of all particles on the surface.
Optionally, only particles that can be expected to cause current or
future damage to the surface are included. Then, using optical
tweezers, each particle is individually removed and then disposed
of. Six different ways to remove particles are described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates the general principle of optical
tweezers.
[0014] FIG. 2 shows a first embodiment of the invention in which a
contaminant particle is removed from a downward facing surface.
[0015] FIGS. 3-7 show five variations of a second embodiment of the
invention in which a contaminant particle is removed from an upward
facing surface.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Since optical tweezers have proved to be an effective tool
for three dimensional trapping and manipulation of particles, the
present invention uses them as its means for removing contaminant
particles from the surface of an integrated circuit wafer. The
process of the present invention can be divided into three main
steps:
[0017] (1) Detect and record the location and size of all
contaminant particles or, optionally, only selected particles that
are predicted to reduce product yield. Typically, particles have a
mean diameter between about 0.12 and 0.5 microns, with about 1
micron being an upper limit to what can be handled by optical
tweezers at the current state of the art. In the 0.15 micron
process, any particle whose size exceeds about 0.25 microns is
likely to cause a yield loss. This step is accomplished by using an
in-line inspection tool. An example of this is KLA which was
mentioned earlier. Optionally, the same lens system used to
generate the optical tweezers may also be used for obtaining said
positional co-ordinates.
[0018] (2) Using the optical tweezers, access each location
separately and remove all, or only selected, particles from the
semiconductor wafer surface, depending which takes least time
(including the time to execute step 1). As a practical matter, the
optical system needs to have a NA of at least 0.8 and the light
source needs to be a laser (such as Ar or he-Cd) operating with an
intensity of at least 10 W.
[0019] (3) Dispose of the removed particles, usually, though not
necessarily, by reducing the power level (including full turnoff)
until the particle is drawn out of the trap by gravitational
forces.
1.sup.st Embodiment
[0020] Referring now to FIG. 2, we show there the first of two
embodiments of the invention. Schematically represented is silicon
wafer 21 whose lower surface 22 contains one or more integrated
circuits. Contaminant particle 14 is seen after it has been drawn
away from surface 22 by the light trap 13 at the focal point of
focused laser beam 16. This was accomplished by first positioning
the lens (12 in FIG. 1) so as to bring the focal point of
converging beam 16 directly below where the particle 14 had been
sitting on the surface 22 at a distance from the particle of
between about 200 and 500 nanometers.
[0021] Positioning of the beam 16 was, in turn, achieved by
controlling motion of the lens from a data base that contained the
coordinates (on the wafer surface) of all particles that were to be
removed. Depending on the relative times to populate the data base
and to remove particles, all particles on surface 22 could be
removed or removal could be limited to particles that, because of
their position on the surface, were expected to damage the
integrated circuit, either immediately, during later processing, or
on life.
[0022] A key feature of this embodiment is that a stream of gas
(symbolized by arrow 25) is caused to flow past and around wafer 21
in a downward direction. As a consequence, when the power level of
the laser is reduced (or made zero), there is no longer sufficient
force within the light trap to hold the particle and it gets swept
away from the wafer through a combination of gravitational forces
and the carrying power of the gas stream.
2.sup.nd Embodiment
[0023] Referring now to FIG. 3, the first of several variations of
the second embodiment is shown. Schematically represented is
silicon wafer 21 whose upper surface 22 contains one or more
integrated circuits. Contaminant particle 14a is seen after it has
been drawn away from surface 22 by the light trap 13a at the focal
point of focused laser beam 16a. This was accomplished by first
positioning the lens (12 in FIG. 1) so as to bring the focal point
of converging beam 16 directly above where the particle 14 had been
sitting on the surface 22 at a distance from the particle of
between about 200 and 500 nanometers.
[0024] Positioning of the beam 16 was, in turn, achieved by
controlling motion of the lens from a data base that contained the
co-ordinates (on the wafer surface) of all particles that were to
be removed. Depending on the relative times to populate the data
base and to remove particles, all particles on surface 22 could be
removed or removal could be limited to particles that, because of
their position on the surface, were expected to damage the
integrated circuit, either immediately, during later processing, or
on life.
[0025] Variation 1: Continuing our reference to FIG. 3, it is seen
that disposal of the removed particle 14a is achieved by moving the
focal point 13a of the laser to position 13b where particle 14b is
no longer above the wafer surface. The laser power level is then
reduced or terminated causing particle 14b to be removed by
gravity.
[0026] Variation 2: Referring now to FIG. 4, as in variation 1,
disposal of the removed particle 14a also begins by a lateral
movement of focal point 13a to a new position 13c. Unlike variation
1, however, 14c is higher than 14a and continues to be above the
wafer. A key feature of variation 2 is that catcher plate 41 is
then inserted between focal point 13c and the surface so that when
the power level is reduced or terminated, the particle falls onto
the catcher plate which is then removed.
[0027] Variation 3: Referring now to FIG. 5. This resembles
variation 1 in that the light beam and particle do not move.
Instead, wafer 21a is moved to position 21b which is sufficiently
removed from 21a so that particle 14 is no longer above the wafer
surface. The laser power level is then reduced or terminated
causing particle 14 to be removed by gravity.
[0028] Variation 4: This is illustrated in FIG. 6. Unlike the
previous three variations, neither the focal point nor the wafer
get moved. Instead, tube 61 is provided. This has one open end with
the other end being connected to low pressure chamber 62, low
pressure meaning a pressure lower than that at focal point 13. Tube
61 is brought into position so that its open end is close to
particle 14 at which point the particle gets pulled out of the
light trap, moving along direction 63 and getting sucked into tube
61 and thence into low pressure container 62. Typically the
pressure at focal point 13 would be about atmospheric or low
pressure chamber 62 could be used.
[0029] Variation 5: This is illustrated in FIG. 7. Here too neither
the focal point nor the wafer get moved. Instead, tube 71 is
provided. This has one open end with the other end being connected
to pressure source 72. Tube 71 is brought into position so that its
open end is close to particle 14 at which point the particle gets
pushed out of the light trap, moving along direction/trajectory 73
and not falling below the level of surface 22 until it is clear of
the wafer. Typically the pressure at focal point 13 would be about
atmospheric.
[0030] While the invention has been particularly shown and
described with reference to the preferred embodiments thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made without departing from the spirit
and scope of the invention.
* * * * *